Experimental assessment of the kinetic parameters of the JSI TRIGA reactor

An experimental campaign has been carried out at the TRIGA reactor of the Jozef Stefan Institute, in order to assess its mean neutron generation time Λ and effective delayed neutron fraction βeff. For that, the cross spectral densities (CPSD) of two fission chambers have been taken. The reactor has been operated in five core configurations corresponding to different control rod and chamber positions. A method of comparison between the cross spectral densities using the Welch statistical test, without assuming any kinetic model, has been performed; it shows that it is possible to distinguish between those configurations provided an high enough integration time (above 3000s) is used. Assuming a point-kinetic model, the parameters Λ and βeff have been robustly derived by a Cohn-α technique. The generation time is found to be rather constant from a configuration to another, but configurations with different fuel loading and control rod position yield an effective delayed neutron fraction that differ at 1σ level. The experimental values for both parameters agree with the values provided by the TRIGA manufacturers.